Biphasic Binder/Aggregate Framework for Geomaterial Ductility

ABSTRACT: Critical applications of geomaterial modeling often require a computational framework unifying two key features: (1) physically realistic stress-strain nonlinearity due to pressure sensitive dissipative phenomena, and (2) robust and efficient computation of the material constitutive response, particularly for coupled modeling of damage-plasticity with frictional contact. A diverse range of geomodels demand both nonlinear material physics and numerical tractability: pressure-induced com- paction/dilation in oil and gas reservoirs; fracture-network near-wellbore process evolutions in geothermal systems; and, impact event-driven dynamics in soil, hydride, rock, and manufactured formations. In particular, contact simulations need a fast and reliable geomaterial model because numerically intensive (e.g., requiring fine spatiotemporal discretization to resolve fault slip, closure of existing cracks, and/or interaction dynamics of fragmentized rock). One pathway to enhance the robustness and efficiency of nonlinear computational geomechanics, but retain physics necessary to approximate complex coupled phenomena like contact, is adoption of an optimization framework for geomaterial path-dependent constitutive relations. In this work, a two-phase or "biphasic" minimization algorithm for pressure-sensitive nonlinear ductility is described, calibrated, and exercised in a dynamic geomechanics model incorporating challenging contact conditions. Focus is provided to multi-surface plasticity modeling of decohesion during brittle-ductile transition, via a separation of stress contributions into "binder" and "aggregate" material phases yielding effective plastic nonassociativity (Bryant et al., IJNAMG, 2022 and Bryant et al., 56th USRMGS, 2022).